Stop flutter device



April 28, 1936. J HE 2,038,603

STOP FLUTTER DEVICE Fil ed March 2, 1955 (/E/l/V ,4 /Qo CHE Patented Apr. as, '1936 UNITED STATES I PATENT OFFICE. I $3522 mm Jean A. Roche, Dayton, Ohio Application March 2, 1935, Serial No. 9,Il62

Claims.

(Granted under the act of March 3,1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment tome of any royalty thereon. 5 My invention is intended for attachment to any structure suspected of developing dangerous flutter.

When so installed, the device serves a twofold object. It furnishes positive evidence of the presence or absence of dangerous flutter and further stops the aforesaid flutter in its incipient stages.

The device is particularly adapted for mounting upon the wing tips, fixed surfaces, struts or wires of aircraft, either internally or externally as space permits with respect to the particular flutter element with which it is associated. It is also applicable to vehicles other than aircraft. I

As originally developed, the device was primarily intended as a safety measure for use in Y diving or high speed tests of airplanes in which the structural strength is known to be satisfactory, but in which it is feared that a resonant flutter may build up. to destructive proportions. With the foregoing andother objects in view, which will appear as the description proceeds, the invention consists of certain new and novel improvements in stop flutter devices, which will be hereinafter more fully illustrated and described in the accompanying. drawing and more par- 0 ticularly pointed out in the appended claims.

' Referring to the drawing, in which numerals of like character designate similar parts throughout the several claims:

Fig. 1 is a side view of the device attached to i 35 the tip of an airplane horizontal surface.

I Fig. 2 shows application of the device to the tip of an airplane stabilizer.

Fig. 3 isa cross-sectional view of the arresting portion of the device.

9 Fig. 4 is a plan view of the arresting portion.

It is well known to those skilled in .the art that vibration in any structure can be dampenedout by a device consisting of a counterweighted spring rigidly connected to a predetermined portion of g 45 the vibrating structure. It is essential that the aforementioned springassembly be adjusted such that it is tuned to the natural frequency of the flutter element to which it is attached. It so tuned, when flutter occurs, forces'will be set up 50 by the weight and spring element which will neutralize the flutter, thus preventing resonant flutter building upto a destructive stage. It'is an object of-this invention to function not only as a stop flutter device, but also as a device for determining whether or not the structure to as to render it inactive, at the will of an aircraft pilot, in order to permit structural flutter to come 5 into being, through the medium of secondary air forces or engine vibration.

Fig. 1 shows cantilever spring I pivotally secured to any surface 2 suspected of developing dangerous vibration by means of a hinge pin 3 10 and mounting bracket 4. At the outer extremity of the cantilever spring I are mounted a plurality of washers 5, by means of a bolt 6, a not I and a cotter pin 8. The aforesaid assembly of parts may be said to compose a counterweight 9, of pre- 15 determined mass: Momentarily considering the inner end of the spring I to be fixed, the combined structure of the outer or overhanging portion of the cantilever spring I and the counterweight 9 is so proportioned that the vibration 20 frequency thereof will be identical to the vibration frequency of the surface 2, when the latter is the normal adjustment for my invention durmg the initial stage of aircraft flight. It is not essential at this point to enumerate the various functions performed by the device I0. Attention, rather, will be devoted to the remaining secondary improvement incorporated in Fig.1. It will be noted that the bracket 4 projects beyond the tip extremity-of the surface 2 in an arm II. The outer end of the arm II is provided with a wing bolt I2 and lock nut I3. The foregoing parts have been added in order that, in a state of rest, the 40 inner extremity of the cantilever spring I may be maintained in operative alignment with the device III. Were it not for the aforementioned improvement, the outer extremity of the cantilever spring I would fall downward until it contacted the tip extremity of the surface 2. Care must be taken, however, that the upper extremity of the wing bolt I2 does not'interfere with the dampening motion of the cantiliever spring I and. attached counterweight 9; It may be found .50

the inner end of the cantilever spring I to move out of alignment with the device It. The spring I4 may also be eliminated through flxity of the top and bottom extremities of the spring ii to the lever I and surface 2, respectively. All of the aforementioned refinements are of secondary importance. It is of primary importance that the cantilever spring I and counterweight 9 be hinged about the pin 3 such that with the device I0 dis engaged, the vibration frequency thereof shall be appreciably different from that of the surface 2.

It is essential, at this point, that the composition and operation characteristics of the latching device III be disclosed. In Fig. 3, a housing It is provided with a bolt IT. The forward extremity of the bolt I1 is provided with a V-shaped notch I3 adapted to fixedly engage the inner extremity of the cantilever spring I, when projected from the housing I8, in order that the spring be held rigid with respect to the surface 2. The central portion of the bolt I1 is extended rearwardly through an opening in the housing iii to form an arm I9. The rear face of the bolt I1 is provided with holes into which are inserted springs 2|. Guide pins 22 are fixedly secured to the rear face of the housing It, coaxial with the V-shaped notch thereof. A pin the springs 2|, in order that be held in proper alignment the V-shaped notch I3 of the bolt I! from the forward extremity of the housing I 3. The upward forward portion of the housing I 8 is cut away to provide for installation of a counterweighted lever 23. The forward lower extremity of the counterweighted lever 23 is provid with a sear 24 adapted to operably engage a sea v seat 23 provided in the upper forward portion of the bolt I I. As shown in Fig. 3, the sear 24 and sear seat 23 are in "fixed engagement, thus securing l3 from protruding from the housing It. The counterweighted lever 23 is provided at its rear with a weighted disc 23, having slotted opening 21 permitting free passage of the arm I3 to the rear 28 secures the forward extrem ity of the counterweighted lever 23 to the housing II.

It will be noted that when the -.bolt I 1 is compressed entirely within the housing I 6, through the springs 2| may during protrusion of forward face of the the exertion of tension upon the arm IB-by means of a hole 29 and a cable 30 shown in Fig. 2, gravity will cause the counterweighted lever 23 to assume the position shown in Fig. 3, in which escape of the bolt I I from its recess within the housing I 6 is prevented by the sear 24 and sear seat 25. If the structure to which the device I0 is secured is suddenlysubjected to a sharp down-- ward blow, or series of equivalent oscillations, inertia within the weighted disc 26 will cause disengagement of the sear 24 from the sear seat 25. It will be noted that the vertical dimensions of the opening 21 are Just suflicient to ermost surface of the sear contact with the upper rear surface of the bolt l1. Through the aforementioned limitation, the counterweighted lever 23 is secured against movement relative to the housing It whenever the V-shaped notch ll of the bolt I'l protrudes from said housing.

It is essential to the operation of the device In that the v-shaped notch It be automatically projected from the housing I3 at the very inception of vibrations of predetermined magnitude in the surface to which the device III is fixedly attached. It is only through the foregoing charpermit the low- 24 to lie in intimate bracket 4 and housing I6.

acteristic that dangerous flutter may be dampened out before reaching a destructive magnitude. It is a second essential of the device III that the pilot of the aircraft be able during flight to cause manual engagement of the device III with the inner extremity of the cantilever spring i. Double precaution must be exof diving or high a still further esthat following execution of the above or other predetermined maneuver, that-the pilot may at will disengage the device ill from the inner extremity of the cantilever spring speed tests is involved. It is sential of the device I 0 I. This final design feature permits utilization J of the device III as a telltale, the pilot's manual control being so constructed and arranged as to indicate engagement of the device I 3 with the inner end of the cantilever spring I.

26 of the counter-weighted lever 23 until the lower surface of the opening 21 is brought into contact with the lower surface of the arm I3. As shown in Fig. 2, it will be noted that slack occurs in a cable 36 secured to the upper Portion of the lever 33 by means of a hole 35 for the reason that this particular figure illustrates inertia release of the v-shaped notch I3 from the housing I3. When pilot release is effected, the cableassumes a straight line between the hole 35 and the tandem pulleys 3 I, from whence it is led by a further pulley system tothe pilot's cockpit. Gravity is suflicient to force the lower extremity of the lever 33 downward when the pilot manually withdraws the v-shaped notch I8 entirely within the housing It.

Fig. 4 shows a plan view of the device III in which a base 31 is provided with bolt holes 38 for securing the housing I6 to its supporting surface. A vertical flange 33 is provided on each side of the forward extremity of the counterweighted lever 23 to guide same longitudinally with respect tion of the J-shaped lever 33 seeks to retain its initial position with respect to the weighted disc 23' through pivotation about the pin 34. The aforementioned impulse also results in dual pivotation of the lever I about thepin 3 and the about the pin 23'. The latter pivotation has released the notch I 3 from within the housing II, which is seen to engage at its lowermost extremity the inner extremity of the cantilever spring i. It will be noted that the helical spring l prevents the inner extremity of the cantilever spring I from assuming a position below the engaging area of the lower jaw of the notch 18. With. initial issue of the notch Hi from the housing IS, the counterweighted lever 23 is locked with reference to the housing l6, permitting the notch l8 to advance until the inner extremity of the lever I is seated at the base thereof. The longitudinal axis of the inner extremity of the lever I will thus become coincident and fixed in regard to the longitudinal axis of the device l0, remaining thusuntil released by the pilot in the manner heretofore enumerated.

Since my device is inertia actuated, it is obvious that the cantilever spring I, mounting bracket 4, locking device In and helical spring l5 (used in combined tension and compression) of Fig. 1 may be removed from the horizontal installation shown in Fig. 2 and reinstated vertically upon the overhanging upper portion of the fin supporting the rudder 40; with such redisposition of the weighted disc 26, that the sear 24 will engage the sear seat 25, upon tensioning of the cable 30. It is further essential, in the foregoing weight redisposition, that inertia disengagement of the sear 24 be not impaired; i. e., that the center of gravity of the weight be disposed wellbelow the pin 28.

I claim:

1. A stop flutter device for mounting upon a I structure having a knownfrequenoy of vibration comprising, an elongated flexible member having one end predeterminately weighted, a bracket fixedto a predetermined portion of said structure and pivotally attached to said member inboard of the non-weighted end thereof, and inertia operated means for predeterminately positioning said member approximately parallel to said structure such that said unweighted end from bracket to tip is fixed with respect to, but that said weighted end from bracket to tip is flexible with respect to its supporting structure end capable of vibration frequency corresponding to, but in a direction opposite to said known vibrations.

2. A stop flutter device for mounting upon a structure having a known frequency of vibration comprising, an elongated flexible member having one end predeterminately weighted, a bracket fixed to a predetermined portion of said structure and pivotally attached to said member inboard of the non-weighted end thereof, means for predeterminately limiting pivotal movement of the non-weighted end of said member relative to said structure, and a locking device for selectively fixing the aforesaid end against pivotation such that said weighted end from bracket to tip is flexible with respect to its supporting structure and capable of vibration frequency corresponding to but in adirection opposite to said known vibrations.

3. A stop flutter device for mounting upon a structure having a known frequency of vibration comprising, an elongated flexible member having one end predeterminately weighted, a bracket fixed to a predetermined portion of said structure, said elongated flexible member being freely rotatably attached to said bracket inboard of the non-weighted end thereof, and remotely controlled means whereby said elongated fiexible member can be selectively fixed approximately parallel to said structure such that the unweighted end thereof from bracket pivot to tip is fixed with respect to, but that said weighted end from bracket to tip is flexible with respect to its supporting structure and capable of vibration frequency corresponding to but in a direction opposite to said known vibrations.

4. A stop flutter device for mounting upon a structure having a known frequency of vibration comprising, an elongated flexible member having one end predeterminately weighted, a bracket fixed to a predetermined portion of said structure, said elongated flexible member being freely rotatably attached to said bracket inboard of the non-weighted end thereof, and manually actuated means whereby said elongated flexible member can be selectively fixed approximately parallel to said structure such that the unweighted end thereof from bracket pivot to tip is fixed with respect to, but that said weighted end from bracket to tipis flexible with respect to its supporting structure and capable of vibration frequency corresponding to but in a direction opposite to said known vibrations.

5. A stop flutter device for mounting upon a structure having a known frequency of vibration comprising, an elongated flexible member havin one end predeterminately weighted, a bracket fixed to a predetermined portion of said structure and pivotally attached to said member inboard of the non-weighted end thereof, inertia operated means for predeterminately positioning said member approximately parallel to said structure and remotely controlled means whereby said member may be released from the aforesaid position in which said unweighted end from bracket to tip is fixed with respect to, but that said weighted end from bracket to tip is flexible with respect to its supporting structure and capable of vibration frequency corresponding to, but in a direction opposite to said known vibrations.

JEAN AQRQCHE. 

